The present invention relates to lightweight aggregates and in particular to a lightweight expanded polymer used as an aggregate when coated with a mixture formed with dehydrated lime and hydrated alumina and to a method of coating an expanded polymer with the specific mixture preparatory to mixing with cement, sand and water for producing a lightweight construction material.
In the past, concrete blocks and other materials have been manufactured by mixing predetermined mixes of Portland cement, sand and water and adding various types of aggregates made from a great variety of materials, such as rock granite and slag from smelting operations. Lightweight aggregates may be produced from slags from the production of phosphoric acid, and the like. Lightweight aggregates have the advantage of producing a lighter building block or material having great strength in compression and with reduced problems of shipping and handling due to the lighter weight and while advantageously providing additional isulation value. The prior art also suggests using a variety of products, as aggregates, as well as various compositions for mixing with aggregates which include the use of polystyrene with a homogenizing agent as set forth in U.S. Pat. No. 3,257,338 for a concrete composition comprising cement, a primary aggregate, expanded polystyrene and a homogenizing agent, the homogenizing agent being an alkali metal salt. The use of a foamed thermoplastic polymer for plastering masonry surfaces is taught in U.S. Pat. No. 3,291,762 and uses flakes of a foamed thermoplastic polymer with up to 97% by weight of a dry filler and minor proportions of drying oil in a solvent. U.S. Pat. No. 3,066,031 teaches a cementous material and method of preparing such material using calcium oxide mixed with a reactant of silicon dioxide and aluminum dioxides while U.S. Pat. No. 3,669,701 teaches a lightweight cement for oil wells which utilizes small cenospheres consisting primarily of silica-alumina. Other compositions may be seen in U.S. Pat. No. 3,076,717 for building load supporting surfaces; U.S. Pat. No. 2,060,295 for an acoustical or insulating plaster; and in U.S. Pat. No. 3,021,291 for preparation of concrete containing expanding polymeric particles in which a concrete mixture of Portland cement is mixed with polymeric material in the form of small particles, including the polymers of styrene and ethylene. U.S. Pat. No. 3,272,765 teaches a lightweight concrete having a lightweight aggregate of closed celled multicellular expanded polymeric particles and a binder containing entrained air. U.S. Pat. No. 3,214,393 teaches a concrete mixture containing expanded polystyrene and homogenizing agent in which cement, a primary aggregate, expanded sytrene polymer and homogenizing agent consisting of polyvinyl alcohol and a bituminous compound and the alkali metal salt of the aliphatic insoluble portion of the aromatic extract of pinewood are combined. U.S. Pat. No. 2,517,993 teaches a hydraulic cement composition of Portland cement, burned slag and other materials while U.S. Pat. No. 3,679,445 teaches a low density concrete having Portland cement and high alumina cement along with a fine aggregate and a course aggregate and short fibers and air entrained therein. U.S. Pat. No. 3,498,809 teaches a finishing mortar composed of a filler binder in water and utilizing an inorganic gel which is a reaction product of an inorganic base and a metal salt along with a water soluble cellulose derivative. United Kingdom Pat. specification No. 836,499 teaches improvements to lightweight concrete and aggregates in which a nonbrittle cellular springy particle of porous material are dispersed substantially uniform through a construction material.
In contrast to the prior patents, the present invention teaches a mixture used to coat expanded polystyrene beads, or the like, which have obtained high thermal resistant qualities and compressive strengths. The present coating of expanded polystyrene beads improves the quality and physical characteristics of a concrete product using expanded polystyrene beads as an aggregate.